Conventionally, it is known that various colored substrates (such as printed articles, building materials, fibers, organic polymer resin products, and the like) become faded and discolored over time. Factors in such fading and discoloration include photodegradation, adhesion of contaminants to the surface of the substrate, and the like. Various methods have been developed as countermeasures therefor.
For example, in order to prevent photodegradation, a method in which an ultraviolet absorber is mixed in a substrate has been adopted.
Moreover, in order to prevent or remove adhesion of contaminants from the surface of a substrate, a method in which a coating film having an anti-contamination function or a self-cleaning function is formed on the surface of a substrate has been developed. An example of the aforementioned method is a method in which a photocatalytic layer is formed by employing anatase-type titanium oxide, described in Japanese Unexamined Patent Application, First Publication No. H09-262481.    Patent Document 1: Japanese Unexamined Patent Application, First Publication No. H09-262481